1. Field of the Invention.
The present invention relates to magnetic actuators where deflection of a member is a linear function with respect to an input current to the actuator.
2. Description of the Prior Art.
Magnetic actuators that provide a deflection as a function of electrical input signals are used in a variety of applications. A typical electrical signal to pressure signal transducer is shown in U.S. Pat. No. 4,534,376. The actuator of the present invention provides improvements to the actuator shown in FIG. 6 of this patent, and the preferred embodiment disclosed herein can be used for general applications where small displacements as a function of low input currents is desired.
In particular, it is desirable to have very low power levels developing the actuator forces and deflections. The amount of measurable deflection available in the small size actuator should be as much as possible (the working gaps should be large) to reduce manufacturing tolerance requirements and lower cost. The device of the present invention achieves these objectives.
U.S. Pat. No. 3,946,757 shows a pneumatic actuator used as the fuel metering valve that has a permanent magnet that establishes a magnetic flux across a gap, and a valve control armature is mounted for movement in the gap. The armature is pivotally mounted, and its lower portion is spring loaded to resist movement about the pivot. A coil is placed around a portion of the armature to create an actuating flux field that moves the armature as a function of the current in the coil. This device does show a coil that provides displacement of an armature positioned in a gap of a permanent magnet and the flux provided by the current in the coil adds to the permanent magnet flux on one side of the armature, and subtracts from the permanent magnet flux on the other side of the armature.
U.S. Pat. No. 3,004,546 shows an electromagnetic transducer which utilizes permanent magnets around a central body, and a coil that provides a magnetic flux in the central body that will add to the flux from the magnets in one direction, and subtract from the flux of the permanent magnet in an opposite direction of deflection. The actuator is a force balance, electropneumatic device and the actuation force is axially along the coil. The magnets do not provide for flux paths that are used with a deflecting diaphragm type spring as shown in the present disclosure.
U.S. Pat. No. 3,913,608 also shows a valve actuator that uses both permanent magnets and electromagnets for operation, but this device is intended to be a valve actuator unit having two valve positions, either open or closed, and there is no requirement that the current be proportional to the displacement of an a actuator as in the present device.
U.S. Pat. No. 4,018,419 also shows an on/off valve utilizing both permanent magnets (a magnetized valve rod) and a coil that moves the magentized rod and when the coil is not energized, the magnetized rod is moved to hold the valve open, while energization of the coil will close the valve.
U.S. Pat. No. 4,053,137 shows an electromechanically operated valve that has a valve member that is spring mounted, and which is actuated by an electromagnetic actuator responsive to current in a coil.
U.S. Pat. No. 4,306,589 shows a low power solenoid operated air valve with magnetic latching, that has a permanent magnet in the installation, as well as an electromagnet, which cooperate together for valve operation. The permanent magnet forms a valve member that is seated upon one or the other of two nozzles in response to the electromagnetic field.
U.S. Pat. No. 3,216,938 also shows a solonoid actuated valve device utilizing both a permanent magnet and an electromagnet for operation. The device does control a flow of fluid in proportion to the electric current, and does not embody the arrangement utilizing a diaphragm type spring (although it has a coil spring) or the arrangement of the magnet and flux gaps used in the device of the present device.
U.S. Pat. No. 4,310,143 also shows an electrically controlled proportional valve for hydraulic applications, including means for establishing a static magnetic field within the valve body, and also an electromagnetic device for inducing a magnetic field within magnetizable portion of the valve member so that the induced magnetic field interacts with the static magnetic to position the valve member axially. The position is controlled as a function of the energization current of the electromagnetic device. This linear actuating spool has a coil centering spring, and controls fluid flow as a function of the current.
U.S. Pat. No. 4,428,558 also shows a proportional solenoid valve comprising a rotary magnet causing a rotational displacement within an angle of 180.degree. in proportion to the current being supplied to the coil, with a torsion bar for dampening the rotation.
An on/off magnetically actuated pilot valve is shown in U.S. Pat. No. 4,366,944. This valve is used as an armature plate that is movable between two positions, one closing off fluid pressure and the other closing off the connections to drain. Spring bias is used for biasing the armature plate to one of the positions. Current in the coil moves the plate to the other position.
U.S. Pat. Nos. 3,878,504, and 4,285,054 relate to "geophones" which comprise an annular coil-mass and a permanent magnet assembly positioned inside the coil coil-mass with their longitudinal axis generally coinciding, and spring spiders are used for supporting the coil-mass. The permanent magnet, and the actuator core of the electromagnet are arranged such that the coil-mass is supported within the permanent magnet assembly for axial and rotational movement.
Dampening fluids are also provided in U.S. Pat. No. 3,878,504. The device does show diaphragm type spiders used as springs, but not the sandwich construction of the present device, nor do they show actuators positioned for movement as disclosed herein.
U.S. Pat. No. 4,206,749 shows a control system utilizing permanent magnet assemblies for actuation. A polarizing magnetic field is provided for actuating this device.